# Full text of "Development of Switch Mode Dc Converter Using MATLAB/ dSPACE"

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```ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 03, October 201 1

Development of Switch Mode Dc Converter Using

MATLAB/dSPACE

First A. P.Srikanth 1 , Second B. Dr R.Saravana Kumar 2
1 VIT University, School of Electrical Engineering, Vellore, India

Email: psreddyl988@yahoo.com
2 VIT University, School of Electrical Engineering, Vellore, India

Email: rsaravanakumar@vit.ac.in

Abstract — In this paper with the help of Matlab/Simulink and
dSPACE, the Switch-Mode DC Converter is built in real-time
to control the output voltage of the controller using PWM
algorithm. First, the Simulink model of Switch-Mode DC
Converter (i.e. Single-Pole and Two-Pole Converter Model)
is built and, after verifying the results, it is implemented in
real-time. Next, a DC motor is connected to the output
terminals (i.e. Phase At and Phase Bl) of the Power Electronics
Board such that a variable voltage is applied to the terminals
of DC motor. Now, by changing the magnitude of the applied
voltage, the speed of the motor is varied. This is also referred
to as an open-loop voltage control of DC motor. The purpose
of the real-time implementation is obtaining variable voltage
at the output of the power converter, while controlling its
amplitude with a dSPACE DS1104-based user interface.

Index Terms — Single-pole, Two-pole, dSPACE.

I. Introduction

In the switch pole converter circuit, the input voltage and
output load are assumed constant. The switching power pole
operates with a switching function q A (t), whose waveform
repeats, unchanged from one cycle to the next, and the
corresponding switching duty ratios are constant at its DC
steady-state. The output pole voltage V m (t) is either V d (input

voltage) or depending upon the position of the converter
switch. Theconverter switch is pulse-width modulated by
comparing triangular waveform with the control voltage

V . There are two such PWM strategies, one is PWM with
unipolar voltage switching in this, switches in each leg are
controlled independently of the other leg and another one is
PWM with bipolar voltage switching, in this, switches in
each pair are turned ON and OFF simultaneously. The
objective is to develop a real time model using dSPACE
DS1 104_DSP_PWM3 to obtain variable voltage at the output
of the converter for controlling speed of the DC motor. The
dSPACE provides complete solutions for electronic control
unit (ECU) software development and it is powerful
development tools for dedicated services in the field of
function prototyping, target implementation, and ECU testing.
Real time control systems can be built using dSPACE and the
control logic can be implemented and works on Matlab/
Simulink platform. Here the speed of the DC motor is
controlled by Pulse Width Modulation (PWM) technique to
obtain a smooth speed variation without reducing the starting
torque of the motor.

DOI:01.LICSI.02.03.197

II. PWM TECHNIQUES OF POWER POLE CONVERTER

Controlling the pulse width of the switching function q A (t)
can be accomplished using a technique called Pulse Width
Modulation (PWM). In this technique a control voltage V (t)
is compared with triangular waveform signal to obtain q A (t).

tf v c, A ( t )> v tn ( t )^q A ( t ) = 1
if v c , A (t)<v M (t)*q A (t)=o

The average output voltage V AN (t) of the power-pole with
respect to duty ratio over one switching cycle is given by
V AN (t) = q A (t)*V d

A.PWM with unipolar voltage switching

The uni-polar switching converter [4] shown in fig.l
consists of single pole. The output pole-voltage, V AB (t) of
the unipolar converter is either V d (input voltage) or 0,
depending upon the position of the bi -positional switch and
the pole switching function q A (t).

The duty ratio for a single PWM pole is given by the
equation.

in it- \

■i ■ -i ■ -i.

port

*i «

AAA

r rW«

.X

Ay

id

Olffi'W
port

*i»

Figure 1. Single-pole converter

29

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ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 03, October 201 1

• cl

■ ..»

— t~~ i — i~n i—

■ i i ■

q s i r i

^jj La.: :

-F=wn r .

Figure 2. Unipolar voltage switching

For V = IV we obtain the relation for the control voltage

v c , A (t).

,,, 2v AN (t)

VcA*) = —y - l

B. PWM with bipolar voltage switching

In two pole converter model [4], the average output
voltage V (t) can be positive or negative. The DC converter
consists of two switching power poles as shown in Fig. 3.

The converter average output voltage is the difference
between the two pole output voltages, measured with respect
to the DC bus ground.

v (t) = V AB (t) = V AN (t) - V BN (t)

The output voltage V AB (t) as shown in fig 4. At any given
instant of time, the control voltages for the two poles are
complimentary, i.e.

r(0

I'^<0 - -V«*CO

d*(0 = ^ (>**<*) + 1)

d B {t) = ^ (- ***M + 2 )

u

vj**

V

*

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f V\ 1

7™-

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rs.

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i .

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ff

l£

Figure 4. Bipolar voltage switching

II. Simulation Of Dc Switch Mode Converter

A. Simulink Model for Single Pole Converter

The simulink model is implemented to obtain the duty
ratio and switching function for the single pole converter
model shown in Fig 5. The control voltage c A (t) is compared
with triangular waveform using a relay block. The output of
relay is set to 1 if the difference between control voltage and
triangular signal is positive, otherwise 0. The values of DC
bus voltage (V = 42) and switching frequency (fsw = 10000)
are set at the Matlab command prompt before the simulation.
The desired voltage V AN , with respect to the negative dc-bus
ground is set by a constant block with the value of one, and
can be varied with a slider gain from '0' to the maximum de-
bus voltage V d (42V). The duty ratio and switching function
waveforms of single-pole converter model are shown in Fig.
6.

f-l .1

u

*

: :

c

* |[

:,..

■ r

•H

ttian

ill)

■fott

t*w

fail

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-■■:

Figure 5. Simulink model of switching function and duty ratio
generation of single pole converter

Figure 3. Two-pole DC converter

DOI:01.LTCSI.02.03.197

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ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 03, October 201 1

Figure 6. Switching function qA and duty ratio q A

B. Simulink Model for two - Pole Converter

Simulink model of two pole converter in Fig. 7 is the
comparison of two control voltages V CA (t) and V (t) with
triangular waveform. The Switch block, which allow the upper
signal to pass when the middle input is greater than the
specified threshold and the lower signal in the opposite case.
The Relay block provides the switching functions for the
poles q A and q B . The converter output voltage will be the
difference between the two pole-output voltages, measured
with respect to the dc-bus ground In the two-pole converter
model the output voltage is determined with two slider gain
values. Fig. 8 presents the output voltage and duty ratios
when the slider gain was set to positive value. In the Fig. 9
the output voltage and duty ratios are calculated when the
slider gain value was set to negative value. The input is the
desired average output-voltage V AB . The instantaneous
output voltage will be a square wave signal and the average
value will be equal to the value set by slider gain. By varying
the value of slider gain (i.e. vary the desired average output
voltage value), the output voltage value changes.

r~ — i -I

* \. * ■ *

.... * .

Ww"

<r.a n* J

u 3

Figure 7. Simulink model of switching function and duty ratio
generation of two pole converter

DOL01.UCSI.02.03.197

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u

j

J>

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M

■

M

IH <•

tt l> H It . 1 u to if

n J u ii * « i 'J

i* 1 ™x

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Figure 8. Two-pole converter model with Vout = +10v

Figure. 9 Two-pole converter model with Vout = -10V

C. Simulink model for Real time two pole Switch mode
converter

After obtaining the results of duty ratios and output
voltage for the two-pole converter in the Simulink, this
converter is implemented in the real-time on dSPACE DS 1 1 04
controller board. In the real-time model the converter output
voltage can be controlled with the help of dSPACE control -
desk.

The triangular waveform generator and the comparator
for all converter poles of Fig 7 can be replaced with
DS1104SL_DSP_PWM3 [2] block provides by dSPACE. The
duty ratios served as the inputs to DS1 104SL_ DSP_PWM3.
The Fig. 10 presents the two - pole converter model in real-
time.

;.i ■ .i

*■:.■

EH 1

"**

Figure 10. Two Pole Switch-Mode Converter Model in Simulink

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ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 03, October 201 1

IV. Implementation of switch mode dc converters in dc
motor

The implementation of the model for control of DC Motor
in open-loop as shown in Fig. 1 1 . The DC motor is connected
to the output terminals of the Power Electronics Board such
that a variable voltage is applied to the terminals of DC motor.
Now, by varying the magnitude of the applied voltage, the
speed of the motor is varied. This is also referred to as an
open-loop voltage control of DC motor. The set up has 42 V
dc-bus, two completely independent 3-phase PWM inverters
for complete simultaneous control of two DC machines,
digital PWM input channels for real-time digital control of
dSPACE board. Connect the armature of the dc-motor board
has to be connected to Channel 5 A/D converter of the
dSPACE controller box. The DS1104ENC_POS_C1 and
DS1104ADC_C5 blocks of dSPACE library are used to
measure the speed and current of the DC motor under control
in real-time. Also, the encoder output is connected to the
INC1 9-pins DSUB connector on the dSPACE controller. The
speed of a dc-motor can be modified by varying its supply
voltage. Connect the Lab Oscilloscope to the PHASE A 1 and
PHASE Bl terminals of the motor drives board.

A. Current measurement

For measuring the current we will be using Channel 5 of
the A/D converter in the CP1 104 control board [6] . The motor
drives current sensor IV equals 2 amps so it actually needs
to be scaled by 20. The real-time value of armature current I
for the supply voltage V AB = 40V observed in the Control
Desk window is shown in Fig. 12.

:

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.....

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Figure 1 1 . Real-time model for no-load motor test

DOI:01.LTCSI.02.03.197

91

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CM

1

1

a 1

D t

»s

O "

■ai

111!

Figure 12. Armature Current at V d = 40 V Displayed in the control

desk

B. Speed Measurement

To measure speed of the dc motor use the DS1 104ENC_
and position of the first encoder interface input channel. The
delta position represents the scaled difference of two
angle from the encoder the result has to be multiplied with
2ji/ encoder lines (1000). At low speeds, it was observed
some oscillations in average speed in order to improve the
overall accuracy 1 1 point averaging block is constructed as
shown in Fig. 13. The speed of the dc motor is measured and
displayed in the control desk shown in Fig. 14. The voltage
vs. speed characteristic of DC motor for different voltages at
no-load is measured and verified theoretically as shown in
Fig. 15.

Figure 13. Averaging model in Simulink

300

| 200

mo u i;>j'..

OOIC

OOli

Q 930

Figure 14. Speed of dc motor at V d = 40V displayed in the control

desk

32

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ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 03, October 201 1

3fXi

— HO

=. an
<Si 150

tea

so

•

E

■a

15

3D

2;

3D

38

40

V^mfilCw [V]

Figure 15. Voltage vs. speed characteristics at no-load

Conclusion

In this paper, first, the single-pole and two-pole converter
models are built and simulation results for the positive and
negative values of slider gain are observed. Next, the
comparator and the triangular waveform block of two-pole

converter model is replaced with the DS1 104SL_DSP_PWM3
block and the converter model is implemented in real-time.
Finally, real-time model for speed control of DC motor is built
and the voltage-speed characteristic of DC motor for different
voltages at no-load is measured and verified theoretically.

References

[1] DSP Based Electric Drives Laboratory User Manual, Frequency

Control of A C -Motor Drives, Department of Electrical and Computer

Engineering University of Minnessota.

[2] University of Minnesota, Introduction Getting Started with

dSPACE, DSP Based Laboratory of Electric Drives

[3] Mendrela "Dynamic Simulation of an Elevator driven by dc

motor" Louisiana State University, Baton Rouge, LA.

[4] Ned Mohan "first course in power electronics and drives "

Third Edition, 2003.

[5] Bimal K.Bose, Modern Power Electronics and AC Drives, ©

2002 Prentice Hall PTR.

[6] "ELECTRIC DRIVES an integrative approach" by Ned Mohan,

2000, MNPERE.

[7] Control Desk Experiment Guide, dSPACE, May 2002.